1. College of Arts and Sciences, J. F. Oberlin University, Machida, Tokyo 194-0294, Japan
2. Cell Architecture Laboratory, National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411-8540, Japan
3. Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
4. Misaki Marine Biological Station, Graduate School of Science, The University of Tokyo, 1024 Koajiro, Misaki, Miura, Kanagawa 238-0225, Japan